The periodic table of Messier objects

Observing deep-sky objects just got a little bit easier thanks to Tom Urbain’s at-a-glance guide to the targets of the Messier Catalogue

Charles Messier began his catalogue of observing targets in the mid-18th century to list items that would distract him and his assistant, Pierre Méchain, from their real aim of discovering comets. In the centuries since, the targets listed in the Messier Catalogue have undoubtedly become the most observed deep-sky objects in the night sky by amateur astronomers and astrophotographers.

First published in 1781 containing 103 objects, historical research in the 20th century identified a further seven objects that were observed by the French astronomers, bringing the catalogue up to today’s total of 110 targets. To present this quantity of intriguing astronomical objects in a more understandable way, amateur astronomer Tom Urbain has transformed the list into a periodic table.

“There are quite a lot of Messier objects, so I created the infographic to visually organise them into five different groups according to viewing difficulty, from very easy to very hard,” says the UK-based astro-imager. “I based this on using a mid-range telescope, such as a refractor of 8-inch aperture.”

“Each cell contains the Messier object’s number, the best viewing season and the apparent magnitude,” he continues. “The cells are also colour-coded depending on the object type, so it’s easy to see which is a galaxy, a nebula, an open cluster or a globular cluster. Within each difficulty group, the objects are also organised from brightest at the top to dimmest at the bottom.”

The graphic offers structure to the challenge of finding and observing the Messier objects. “It makes the ‘trial and error’ phase that we all go through a little easier when starting out,” says Tom. “Beginners can therefore refrain from trying to observe very faint Messier objects with a 4- or 6-inch telescope and wondering what went wrong when they can’t see anything.”